I hate it when people do this...
However, the word you're looking for is guarantee god dammit.
Alright, fuck it I don't care but this thread is boring so let's go.
The word guaranty is completely obsolete in every context in modern english. Guarentee is the assumed word in every dictionary and context specifically for any monetary debt.
I WILL STAND BY THAT WITH A GUARENTEE GOD DAMMIT.